Error correction circuit and error correction method

Details Error correction circuit and error correction method Error correction circuit and error correction method

1999-05-13

2004-05-18

Decady, Albert (Department: 2133)

Error detection/correction and fault detection/recovery

Pulse or data error handling

Digital data error correction

C714S792000, C375S265000

Reexamination Certificate

active

06738949

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an error correction circuit for decoding digitally transmitted data which has been subjected to trellis coded modulation (TCM).
2. Description of the Related Art
An 8VSB (Vestigial Sideband) modulation system is employed for the terrestrial digital broadcasting in the U.S. References describing the 8VSB modulation system include, for example, “Digital Television Standard”, ATSC, Annex D, 16 Sept. 1995 (hereinafter, “Reference 1”), and “Guide to the Use of the ATSC Digital Television Standard”, ATSC, pp. 96-126, 4 Oct. 1995 (hereinafter, “Reference 2”).
References 1 and 2 describe encoding and decoding of data based on trellis coded modulation (hereinafter, abbreviated as “TCM”) which has been employed for the 8VSB modulation system. A convolutional encoder having 4 internal states is used as a TCM encoder.
FIG. 22
illustrates a transmitter based on the 8VSB modulation system. Referring to
FIG. 22
, the transmitter comprises terminals
5000
,
5004
and
5005
, a randomizer
5001
, a Reed-Solomon encoder
5002
, an interleaver
5003
, a trellis encoder unit
5006
, and a multiplexer (MUX)
5007
. The transmitter further comprises a pilot inserter
5008
, a VSB modulator
5009
, and an RF up-converter
5010
.
A 186-byte MPEG transport strewn (including 1 synchronization byte and 187 data bytes) is input to the terminal
5000
. The randomizer
5001
randomizes data input through the terminal
5000
, and outputs the randomized data. The Reed-Solomon encoder
5002
performs a Reed-Solomon encoding operation on the randomized data, and outputs the Reed-Solomon-encoded data with 20 Reed-Solomon parity bytes being added to each packet. The interleaver
5003
performs a convolution byte interleave operation on the Reed-Solomon-encoded data at a depth which is about ⅙ (52 data segments) of a data field. The interleaver
5003
does not interleave the synchronization byte, and only interleaves the data bytes.
The trellis encoder unit
5006
performs a trellis encoding operation at a code rate of ⅔ on the data from the interleaver
5003
, and maps the encoded data onto an 8-level data series. A segment sync is input to the terminal
5004
, and a field sync is input to the terminal
5005
. The multiplexer
5007
adds the segment sync and the field sync to the trellis-encoded and mapped data, and frames the obtained data so as to output framed data. The pilot inserter
5008
adds a pilot signal to the framed data. The framed data is subjected to VSB modulation by the VSB modulator
5009
, up-converted by the RF up-converter
5010
, and then output through an antenna as an RF signal.
FIG. 23
illustrates a receiver based on the 8VSB modulation system. Referring to
FIG. 23
, the receiver comprises a tuner
5011
, an IF filter and synchronous detector
5012
, a sync and timing generator
5013
, an NTSC interference remover
5014
, an equalizer
5015
, a phase noise remover
5016
, a trellis decoder unit
5017
, a deinterleaver
5018
, a Reed-Solomon decoder
5019
, a derandomizer
5020
, and a terminal
5021
.
The tuner
5011
tunes to and selectively receives the RF signal from the transmitter, and outputs the received signal. The IF filter and synchronous detector
5012
passes the received signal through an IF filter to convert it to a signal having a predetermined frequency. The converted signal is synchronously detected to convert it to a baseband signal. The sync and timing generator
5013
detects a synchronization signal of the baseband signal so as to time the baseband signal. When the baseband signal contains an NTSC co-channel interference component, the baseband signal is input to the equalizer
5015
after the NTSC co-channel interference component is detected by the NTSC interference remover
5014
and removed by a comb filter in the NTSC interference remover
5014
. When no NTSC co-channel interference component is contained, the baseband signal is directly input to the equalizer
5015
. The waveform of the baseband signal is equalized by the equalizer
5015
, and any phase noise contained therein is removed by the phase noise remover
5016
, after which the baseband signal is input to the trellis decoder unit
5017
as encoded data. The trellis decoder unit
5017
performs a trellis decoding operation on the encoded data and outputs the trellis-decoded data. The trellis-decoded data is subjected to a convolution byte deinterleave operation by the deinterleaver
5018
, a Reed-Solomon decoding operation by the Reed-Solomon decoder
5019
and a derandomizing operation by the derandomizer
5020
, and then output through the terminal
5021
.
Such a receiver unit may employ the following methods for decoding data which has been encoded by a 4-state trellis encoder: a method in which the encoded data is decoded based on state transitions among 4 states, in the case where a comb filter is not used (no NTSC co-channel interference component is contained); and a method in which the encoded data is decoded based on state transitions among 8 states, in the case where a comb filter is used (an NTSC co-channel interference component is contained). The 8 states comprise states resulting from the trellis encoder and other states resulting from the comb filter.
The decoding operation for use with TCM is described, for example, in Japanese National Phase PCT Laid-open Publication No. 10-502776 which discloses a trellis coded modulation system for HDTV (hereinafter, “Reference 3”). Reference 3 describes a decoding method using a 4-state trellis decoder, as a decoding method based on state transitions among 4 states for use in the case where a comb filter is not used, and also describes a method using an 8-state trellis decoder, as a decoding method based on transitions among 8 states for use in the case where a comb filter is used.
FIG. 24
Is a block diagram illustrating a conventional trellis decoder unit for decoding encoded data by selectively using a 4-state trellis decoder and an $-state trellis decoder.
The trellis decoder unit corresponds to the trellis decoder unit
5017
in FIG.
23
.
Referring to
FIG. 24
, the trellis decoder unit comprises terminals
5100
and
5112
, switches
5101
and
5111
, terminals
5101
a
,
5101
b
,
5111
a
and
5111
b
, demultiplexers (DEMUXs)
5102
and
5105
, and multiplexers (MUXs)
5104
and
5110
. The trellis decoder unit further comprises 8-state trellis decoders
5103
a
-
5103
l,
4-state decoders
5106
a
-
5106
l
, postcoders
5107
a
-
5107
l
, adders (modulo 2)
510
a
-
5108
l
, and 1-symbol delay circuits
5109
a
-
5109
l.
The encoded data is input from the phase noise remover
5016
of
FIG. 23
to the terminal
5100
. When the encoded data contains an NTSC co-channel interference component, the switch
5101
is turned to the terminal
5101
a
so as to input the encoded data to the demultiplexer
5102
. The demultiplexer
5102
divides the encoded data by symbols so as to input the obtained data for the respective symbols to the 6-state trellis decoders
5103
a
-
5103
l
, respectively. During a segment sync period (in which the data is not trellis-encoded), no data is input to the 8-state trellis decoders
5103
a
-
5103
l
, while the demultiplexer
5102
switches its selection to the next one of the 8-state trellis decoders
5103
a
-
5103
l
. The decoded data from each of the 8-state trellis decoders
5103
a
-
5103
l
is input to the multiplexer
5104
, where the data is multiplexed together and output to the deinterleaver
5018
illustrated in FIG.
23
.
When the encoded data from the phase noise remover
5016
of
FIG. 23
contains no NTSC co-channel interference component, the switch
5101
is turned to the other terminal
5101
b
so as to input the encoded data to the demultiplexer
5105
. Like the demultiplexer
5102
, the demultiplexer
5105
divides the encoded data by symbols to input the obtained data for the respective symbols to the 4-state trellis decoders
5106
a
-
5106
l
, respectively. During a segment sync period, no data is

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